1. Field of the Invention
The invention relates to a highly integrated electronic circuit, in particular for use in heart pacemakers, defibrillators and the like, comprising a flexible substrate, which has a component side and an insulating bottom side, and an arrangement, corresponding to the circuit function, of active and passive electronic components on the component side of the substrate which are fixed to bond pads of the substrate and connected by strip conductors on the substrate, corresponding to the circuit function.
2. Background Art
As for the background of the invention it is to be noted that in highly integrated electronic circuits, various types of components, i.e. active and passive electronic components, are electrically connected to each other. The substrate consists of an electrically insulating, dielectric material on which bond pads for bonding the components and electric strip conductors for connecting the components to each other are available. Further bond pads can be provided as interfaces for the connection of the highly integrated electronic circuit to external components, such as a power supply, telemetry components and the like. Thus the highly integrated electronic circuit is incorporated into the surrounding field of a certain appliance. Bonding the pads takes place for instance by soldering.
In particular when used in heart pacemakers, defibrillators and the like, miniaturization of these highly integrated electronic circuits plays a very important part. The overall size of these implantable medical devices can be reduced as the compactness of the circuit grows, which, from a medical point of view, leads to simplification of the necessary surgical operations and improved tolerance by the patient.
Fundamentally, the minimization of the number of different manufacturing operations is an object to be achieved with a view to manufacturing rationalization and the simultaneous increase of reliability which is absolutely necessary with these devices.
As regards the prior art, conventional highly integrated electronic circuits are based on rigid ceramic substrates. So as to increase the packing density of the components, their size can be reduced and bonding can be performed in as space-saving a manner as possible. In this connection, SMD (=surface-mounted-device) technology must be cited, in which the surface bonded components no longer have connecting pins. It is also known to use several strip conductor levels one above the other in a substrate as a measure of increasing the packing density.
Further, the prior art teaches circuits which are constructed on flexible plastic substrates. By means of lithographic processes, very narrow strip conductor structures can be applied to such flexible substrates at reduced distances, which can contribute considerably to the miniaturization of the circuit.
U.S. Pat. No. 5,386,341 explicitly illustrates the use of a flexible substrate folded in a U-shape, a rigidizer plate being positioned in the notch of the U of the substrate. Semiconductor components rest on the top side of this sandwich structure, whereas the bottom side is connected via soldering spots to a higher order circuit board. Different temperature coefficients of expansion of the circuit board and the electronic components are compensated by the flexible substrate.
It is further known from U.S. Pat. No. 5,362,656 to wrap a flexible circuit around a rigid metal substrate, the conductors of the flexible circuit being connected to an integrated circuit which is mounted on the top side of the substrate. The flexible circuit has a plurality of metal pads located adjacent to the bottom side of the substrate. The integrated circuit is coupled to the metal pads by way of signal lines in the flexible circuit. The pads can be soldered to a printed circuit board to electrically couple the integrated circuit to the board.